Many processes and devices have been used for wireless communication for the past few years. A number of wireless integrated systems have been introduced for the monitoring and maintenance of industrial process systems. Two of the major products in this area are, for example, the IntelaTrac mobile PKS and the XYR 5000 wireless sensing devices.
The IntelaTrac system, for example, provides a mobile control room for operators in the field in an industrial environment. All process data including current and historical trends, plant layouts, piping and instrumentation diagrams, which are available for the operator in the control room, can now be accessed by the mobile wireless worker in the field. This can be achieved by laying out a wireless Wi-Fi infrastructure in the field and using a web pad that connects to the infrastructure for access to the data much like that found in an office setting. These communications are referred to as “Level 3” (i.e., an indication of the security of the data) communications.
Referring to FIG. 1, a diagram of a prior art system 10 is illustrated indicative of a communication architecture, which can be implemented in an industrial control system. System 10 can be used to manage workflow and field workforce activities 11. As indicated in FIG. 1, an intela trac work process system 12 can be implemented for mobile communication in association with an intela trac mobile manager 13. A wireless LAN (802.11b) provides data synchronization “on demand” for a mobile communication device 15, which provides level 3 communications. A reliability CM system 16 is also provided in association with a maintenance management system 17 and an ERP system (i.e. SAP) 18 with the assistance of an application network (TCP/IP). An operator console module 19 can be configured over the network by using a local control network and an application network (TCP/IP) for operational functionality of the entire system. An alert management system 20 can also be provided, which generates system alerts. Security can be provided by using a firewall 21, whose settings and historical trends are processed by a process historian 22 by enabling configuration with a local control network. A central loop 23 provides a functionality for image processing 25 and for video camera related conferencing.
The XYR5000 and next generation WNSIA based sensor networks also use wireless technologies. Such systems, however, are used to transmit periodic data from sensing elements in the field to controllers that monitor and/or control low level loops. Such a configuration can be referred to as a “Level 1” communication and may be provided through the use of a wireless infrastructure.
The two types of communications (i.e., Level 1 and Level 3) possess different data rates and range requirements. Hence, two wireless networks with different characteristics need to be laid out and implemented. Moreover since these solutions need to be globally applicable, these two networks should preferably operate in the same ISM band (2.4 GHz). This means that for both wireless networks to be operational in a plant, two different infrastructure nodes must be installed in the same plant or location. Also, the security requirements for Level 1 and Level 3 communications are different. As far as possible, these two levels of communication should be kept disjointed from one another. Any device that serves both communication levels should be certified as compliant with different security protocols and should guarantee the Quality of Service (QoS) limits of both networks.
The majority of industrial customers prefer a common integrated infrastructure that is maintainable in the field. Maintenance of the two different infrastructures would be cost prohibitive or may wipe out the cost benefits of a wireless network. One of the problems with prior art systems is that such configurations do not provide for the definition and design of a common infrastructure for a Local Sensor Network and an Application Level Network in the field. Such a system should preferably manage different security protocols depending on the level of the communications that it is serving.
FIG. 2 illustrates a graphical representation 20 with reference to a “backoff time”. In general, the backoff time=Random ( )×a SlotTime, where Random ( ) is equivalent to a pseudorandom integer drawn from a uniform distribution over an interval [0,CW], where CW represents an integer within the range of values of the PHY characteristics aCWmin and a CWmax, wherein aCWmin≦CW≦aCWmax. It is important that designers recognize the need for statistical independence among the random number streams among one or more Slot Times (ST's) and that the SlotTime is equal to the value of the correspondingly named PHY characteristic.
Various types of wireless networks are often co-located or operate in a similar or the same frequency band. A typical wireless public network, for example, may be composed of a plurality of base stations that communicate with mobile stations. Each base station can communicate with mobile stations up to several miles away. Wireless local area network access points can be utilized for communicating with selected mobile stations located in the wireless local area network. An access point can be configured as a first transceiver that communicates with selected mobile stations within a short distance of the access point, a second transceiver that communicates with a first base station of the wireless public network. In such a configuration, interconnection circuitry can also be provided for transferring data traffic between the first transceiver and the second transceiver, such that the access point enables the selected mobile stations to communicate with the first base station via the access point.
A drawback with the use of different wireless networks and/or wireless communications protocols is that interference typically results between two or more wireless networks operating in the same frequency band. A need thus exists for the ability to overcome such interference and allow for the seamless coexistence of two or more networks as disclosed in greater detail herein.